1. Field of the Invention
This invention relates broadly to the field of continuous casting of metals, such as steel. More specifically, this invention provides an improved system and process for monitoring the clamping force that is applied to the mold sidewalls in a continuous casting machine, and a method of controlling the continuous casting machine in response to such monitoring.
2. Description of the Prior Art
Production of metals by use of the continuous casting technique has been increasing since its large-scale introduction about thirty years ago, and now accounts for a large percentage of the volume of steel, among other metals, is introduced each year worldwide. It is well known that continuous casting machines typically include a mold that has two essentially parallel and opposed wide walls, and two essentially opposed narrow walls th at cooperate with the wide walls to define a casting passage of rectangular cross section. Molten metal is supplied continuously into a top end of the casting passage, and the mold is designed to cool the metal so that an outer skin forms before the so-formed slab or strand exits a bottom of the casting passage. The strand is further solidified by secondary cooling sprays as it travels away from the mold, until it becomes completely solidified at or near the end of the continuous casting machine. It may then be processed further into an intermediate or finished metal product, such as steel plate, sheeting or coils by traditional techniques such as rolling.
Continuous casting molds typically have two opposed pairs of sidewalls, one pair serving to clamp against the other, maintaining a fluid-tight joint therebetween. The clamping forces which are initially set by a mold assembly person may vary during the casting operation due to thermal loading. Also, the usual mechanical arrangements for setting clamping forces may be subject to variations caused by human error. Molds which have adjustable sidewalls are in some cases subject to having excess strain exerted on the clamping mechanism due to thermal loading. Also, a clamping force that is larger than necessary may be applied as a safety factor when one clamping mechanism is used for all mold sizes.
FIG. 1 depicts a conventional continuous casting mold assembly 10, in this case of the thin slab type, which includes first and second opposed mold inserts 12, 14 each defining a sidewall 16, 18, respectively. The mold inserts 12, 14 are respectively mounted on first and second support frames 20, 22. In order to clamp the sidewalls together during operation of the mold, the support frames 20, 22 are forced toward one another by at least two tensioning rods 24, each of which is kept in tension by a clamping mechanism 26. A representative clamping mechanism 26, which is identical to one disclosed in U.S. Pat. No. 4,487,249 to When, is depicted in FIG. 2. In this mechanism, one end of the tensioning rod 24 is formed as a threaded boss 28 that is positioned within a threaded recess in a first spring containment block 30. A compression spring 32 that is made of a number of Belleville spring discs is interposed between the first spring containment block 30 and a second spring containment block 34. A compressive load cell 36 is positioned between the second compression spring containment block 34 and the support frame 20. During normal casting conditions, the compression spring 32 will urge the first spring containment block 30 away from the support frame 20, thus placing the tensioning rod 24 under tension in order to clamp the mold. The tensile force in the tensioning rod 24 will be equal to the compressive force that is applied by the spring 32, which is measured by the compressive load cell 36. By monitoring the output of the load cell 36, the system or an operator could determine the clamping force that is applied to the mold, and adjust the clamping force if it was not in a predetermined range.
One way of adjusting the clamping force in a mechanism of the type shown in FIG. 2 would be to apply mechanical force (e.g. a downward force to the first spring containment block 30, as viewed in the figure) in order to counteract some of the force that is being applied by the compression spring. Unfortunately, the load cell 36 shown in FIG. 2 could not accurately measure the tensile force in the rod 24 if the clamping force was so adjusted. The mechanical force would register as additional force on the load cell 36, rendering it unable to measure the actual tensile force that is being applied to the rod 24. A need exists for a clamping mechanism and force monitoring system that is not so limited, and that more accurately reflects the actual clamping force that is applied to the mold under all conditions.